docs: def purge_one(calc_id, user):
      """
      Remove one calculation ID from the database and remove its datastore
      """
      filename = os.path.join(datadir, 'calc_%s.hdf5' % calc_id)
      err = dbcmd('del_calc', calc_id, user)
      if err:
          print(err)
      elif os.path.exists(filename):  # not removed yet
          os.remove(filename)
          print('Removed %s' % filename)